Monday, April 30, 2012

The Military Grid Reference System (MGRS) is a worldwide standard based on Universal Transverse Mercator (UTM) used by NATO to locate points on the earth. More information about MGRS can be found in the Wikipedia.

You can use this mapplet to display the MGRS coordinates for any point on Google Maps. Simply click on any location on Google Maps. Just adjust the Readout Digits to matched the desired MGRS Coordinate accuracy. Alternatively, you can type in an MGRS coordinate in the side bar e.g. 32SMG0329. Then click the Locate point on map button to display the MGRS coordinate on Google Maps.

The default datum used is WGS84. If a different datum is desired, then simple click Datum and select another datum e.g. WGS72.

Tuesday, April 24, 2012

gvSIG's Modeler function can be used to create reusable models of processes that can be applied on geographical vector and raster data layers. For example, if you need to periodically generate centroids and calculate the centroid coordinates from polygon vector layers, then it may be worthwhile to use the Modeler. Once you have a model of the processes created, it is a simple matter to reload the model and run it.

The models are almost similar to programming scripts except that you don't need to be a developer to create them. You simply use a graphical user interface to point and click to define the model. The example below shows how easy it is to create the model with the Modeler.

Monday, April 16, 2012

I spent some time to put together this Google Mapplet that simply shows the latitude and longitude geographic grid lines and labels on Google Maps. The grid lines and labels will display and adjust themselves dynamically as you zoom in and out; from every few degrees until every second.

The screenshot below shows the grid lines and labels at the finest 1 second resolution.

Monday, April 9, 2012

gvSIG has a Photoshop-like tool that can be used to perform geometric transformations on raster files. Transformations such as translation, rotation, scaling, and skewing can be applied interactively to a raster file. The example below illustrates the Geographic Transformation command.

Start the Transformation command

Run gvSIG OADE 2010. Load and display a raster file.

In the toolbar, locate the Geographic transformation icon as shown below.

Then locate and click the Transformation icon as shown below.

The Transformation dialog box appears.

Note: the raster layer can be transformed either by changing the values in the Transformation dialog box or by graphically adjusting the image in the map view.

In the Transformation dialog box, click the Center raster layer in view icon.

The raster layer is scaled, moved and centered in the map view.

Moving the raster image

In the map view. move the cursor to the middle of the raster image.

The cursor becomes a hand.

Press down the mouse left button and drag the image.

The raster image is moved to another location.

Skew the image in the Y-axis direction

Move the cursor to the vertical sides of the raster image.

The cursor changes to an arrow with a Y label.

Press down the left mouse button and drag the image along the Y axis.

The image is skewed in the Y-axis direction.

Skew the raster image in the X-axis direction

Move the cursor to the horizontal sides of the raster image.

The cursor changes to an arrow with the label X.

Press down the left mouse button and drag the image in the X-axis direction.

The raster image becomes skewed in the X-axis direction.

Rotate the raster image

Move the cursor to any corners of the raster image.

The cursor changes to a rounded arrow.

Press down the left mouse button and drag the image around the corner.

The raster image is rotated.

Resize the raster image

Move the cursor along the sides and corners of the raster image.

The cursor changes to a two-headed arrow.

Press down the left mouse button and drag the image inwards or outwards.

Monday, April 2, 2012

There is a function in gvSIG that you can use to georeference any raster images such as scanned images, or photos. The gvSIG georeference function will create world files and other georeferencing metadata information that can be used only with gvSIG apparently. The georeference function has a field to specify the output georeference file but the file is never created. If you want to register raster images for use in gvSIG, then the example below demonstrates the procedure.

Load reference layers and setup the georeferencing views

Start gvSIG. Load and display any geographic features that can be used to aid the georeferencing.